Wire electric discharge machining apparatuses, which machine a workpiece using arc-discharges occurring between a wire and the workpiece, are provided typically in an upper position and a lower position relative to the workpiece, with electrical supply points (current-carrying terminals) from which power is to be supplied to the wire; thus, there exist two parallel circuits: a first one and a second one at the upper and the lower portions of the wire, respectively. A power supply is constituted of two circuits: an auxiliary power supply circuit (an auxiliary electric discharging power supply) for inducing a low-current spark; and a main power supply circuit (a main electric discharging power supply) for supplying a high current that turns out to be a machining current after the spark has occurred.
One of problems associated with wire discharge machining apparatuses is to perform high speed operations in rough machining. Simply stated, increasing machining electrical energy serves the purpose of achieving high speed machining operations. This leads, however, to wire breakage due to concentrated discharges in which discharges occur at one particular part of the wire. As a technique to avoid this concentrated discharge, for instance, Patent Document 1 discloses a technique in which a main power supply is independently connected to the upper electrical supply point and the lower electrical supply point; switching between these two power supply paths leads to discharge positions being made to differ, thereby making it hard for the concentrated discharges to occur. In addition, Patent Document 2 discloses an example configuration using a main power supply circuit and an auxiliary power supply circuit. The auxiliary power supply is connected though a diode (an ng element) to the upper and lower electrical supply points. A ratio of shunt currents that flow through these points determines an electric discharge position, and a power supply is switched from the main power supply, accordingly.
Patent Document 1
Japanese Unexamined Patent Application Publication S59-47123
Patent Document 2
Japanese Unexamined Patent Application Publication S61-95826